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Chapter 4: Primary Hypersomnias

Assessment and Diagnosis

Idiopathic hypersomnia is diagnosed only after ruling out other possible causes, including: Behaviorally-induced ISS, delayed sleep phase syndrome, periodic limb movement disorder, sleep-related disordered breathing, narcolepsy, and secondary hypersomnia.76 In addition, the hypersomnia symptoms may not be caused by a different sleep disorder, medical disorder, psychiatric disorder, or by medication or substance abuse.77

Among those with idiopathic hypersomnia, polysomnography (PSG) shows “short sleep latency, a major sleep period of more than 10 hours, with laborious wakening in the morning or from naps, in the polysymptomatic form, or a major sleep period of 6 to 10 hours in the oligosymptomatic form.”78 The MSLT shows a mean latency of less than eight minutes and no sleep-onset REM periods.79